A Ziegler-Natta catalyst of a titanium or vanadium compound has been used widely in commercial processes for manufacturing polyolefins. The Ziegler-Natta catalyst has high activity but it is a multi-active site catalyst. Therefore, the molecular weight distribution of a polymer prepared by using the same is wide and the distribution of co-monomers is uneven, and there is a limitation in securing desirable properties.
Accordingly, a metallocene catalyst with which a transition metal such as titanium, zirconium, hafnium, and the like and a ligand including a cyclopentadiene functional group are coupled was developed, and has recently been widely used.
Such a metallocene catalyst is a mono-active site catalyst having one kind of active site, and it has an advantage in that a polymer prepared by using the same has a narrow molecular weight distribution, and it is possible to control the molecular weight, the stereoregularity, and the crystallinity, and particularly to drastically control the reactivity of comonomers according to the structure of the catalyst and ligand.
However, a polyolefin polymerized by a metallocene catalyst has a narrow molecular distribution, and there has been a problem in that it is difficult to apply the same to manufacturing because productivity becomes remarkably worse as a result of the influence of an extrusion load when it is applied to some products. Therefore, there have been various attempts to resolve the problem.
[Me2Si(Me4C5)NtBu]TiCl2 (a constrained-geometry catalyst, CGC) developed by DOW Co. in the early 1990's is superior to prior metallocene catalysts known in the copolymerization reaction of ethylene and an α-olefin in that (1) it exhibits high activity at a high polymerization temperature and prepares a polymer with a high molecular weight, and (2) it can easily carry out the synthesis of an α-olefin such as 1-hexene and 1-octene having large steric hindrance.
As such various characteristics of CGC are becoming known, various studies for synthesizing derivatives thereof and using the same as a polymerization catalyst have been actively progressing.
For example, attempts have been made to synthesize a metal compound to which various bridges and nitrogen substituents are introduced instead of a silicone bridge, and polyolefins by using the same.
Representative metal compounds known to date are as follows.

Phosphorous (1), ethylene or propylene (2), methylidene (3), and methylene (4) bridges have been introduced into the listed compounds instead of a silicone bridge of a CGC structure, but they do not give remarkable results in the aspects of activity or copolymerization performance in comparison with a CGC when they are applied to polymerization of ethylene or copolymerization with α-olefins.
Furthermore, many compounds composed of an oxido-ligand instead of the amido-ligand of the CGC have synthesized, and syntheses of polyolefins using them have been partially attempted.
Examples of this are as follows.

Furthermore, synthesis of a catalyst (8) having a similar structure to the above compounds and a high temperature and high pressure polymerization method using the same have been presented by Sumitomo Co.

Meanwhile, Mitsui Co. of Japan developed a group 4 transition metal compound (Ti, Zr) based on a phenoxy imine, and synthesized polyethylene and polypropylene having various characteristics.
It is a specific feature of the catalyst that it does not include a cyclopentadiene ligand which is an important skeleton of prior metallocene catalysts or CGCs in its structure.
Therefore, such catalyst has emerged as a popular post-metallocene catalyst, namely a next generation catalyst breaking away from the metallocene structure.
Since then, this catalyst was named an FI catalyst (10) and has been investigated in detail regarding the catalytic activity and the efficiency according to various substituents changed around the basic skeleton of the catalyst.

Recently, the catalysts (11, 12) having a ligand including another bridge, namely a phenyl group, in a CGC backbone were presented by LG Chem. Ltd. (Organometallics, 2006, 25, 5122 and 2008, 27, 3907).
These catalysts are characterized in that they show activity, content of 1-octene, and molecular distribution which are same as or higher than existing CGCs when they are used to synthesize an ethylene/1-octene copolymer.

However, post-metallocene catalysts applicable to commercial processes in practice are not largely known, and thus, there is still a need to study post-metallocene catalysts which can exhibit higher polymerization performance and can provide polyolefins having excellent properties.